Lines numbering - it's hard to find these days any respectable
editor which does not support this feature.

Word wrapping - can anybody write long scripts without it?

List of recently open documents - ATPad stores this list accordingly
to MAC address, so "Recent Files" on your laptop will look different from "Recent
Files" on your desktop machine! But if you run the program from removable drive and work with
files on this drive, they will be always presented in list, regardless of MAC address of
hosting computer.

Keeping last session - start the work exactly from the point you've
finished (all said above about list of recent documents is true against last sessions as well).

Bookmarks - never lose your way.

Displaying whitespaces - tabs, spaces, line breaks.

Reloading documents "on-demand" - instead of reopening them.

Outer changes tracking - stay informed when any of currently open
documents has been changed out of program.